Plural of blockhead; a foolish or stupid person; someone who is not very intelligent or quick-thinking.
Compound of 'block' (a solid piece of material, suggesting something hard and unchanging) + 'head.' The insult suggests a head as thick and unresponsive as a wooden block, used since at least the 1600s.
The insult 'blockhead' reveals how people use materials to describe character—we call stupid people 'blocks' and 'rocks,' smart people 'sharp,' and clever ideas 'bright,' showing how metaphors of density and light shape how we literally think about intelligence.
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